scholarly journals The Binarity of Early-type Stars from LAMOST Medium-resolution Spectroscopic Survey

2021 ◽  
Author(s):  
Yanjun Guo ◽  
Jiao Li ◽  
Jianping Xiong ◽  
Jiangdan Li ◽  
Luqian Wang ◽  
...  
Keyword(s):  
Orbital Period ◽  
Likelihood Estimation ◽  
Spectral Lines ◽  
Spectroscopic Binaries ◽  
Early Type ◽  
Mass Ratio ◽  
Medium Resolution ◽  
Early Type Stars ◽  
Relationship Of ◽  
The Relationship

Abstract Massive binaries play significant roles in many fields. Identification of massive stars, particularly massive binaries, is of great importance. In this paper, by adopting the technique of measuring the equivalent widths of several spectral lines, we identified 9,382 early-type stars from LAMOST medium-resolution survey and divided the sample into four groups, T1 ($\sim$O-B4), T2 ($\sim$B5), T3 ($\sim$B7), and T4 ($\sim$B8-A). The relative radial velocities $RV_{\rm rel}$ were calculated using the Maximum Likelihood Estimation. The stars with significant changes of $RV_{\rm rel}$ and at least larger than 15.57km s$^{-1}$ were identified as spectroscopic binaries. We found that the observed spectroscopic binary fractions for the four groups are $24.6\%\pm0.5\%$, $20.8\%\pm0.6\%$, $13.7\%\pm0.3\%$, and $7.4\%\pm0.3\%$, respectively. Assuming that orbital period ($P$) and mass ratio ($q$) have intrinsic distributions as $f(P) \propto P^\pi$ (1\textless$P$\textless1000 days) and $f(q) \propto q^\kappa$ (0.1\textless$q$\textless1), respectively, we conducted a series of Monte-Carlo simulations to correct observational biases for estimating the intrinsic multiplicity properties. The results show that the intrinsic binary fractions for the four groups are 68$\%\pm8\%$, 52$\%\pm3\%$, 44$\%\pm6\%$, and 44$\%\pm6\%$, respectively. The best estimated values for $\pi$ are -1$\pm0.1$, -1.1$\pm0.05$, -1.1$\pm0.1$, and -0.6$\pm0.05$, respectively. The $\kappa$ cannot be constrained for groups T1 and T2 and is -2.4$\pm0.3$ for group T3 and -1.6$\pm0.3$ for group T4. We confirmed the relationship of a decreasing trend in binary fractions towards late-type stars. No correlation between the spectral type and the orbital period distribution has been found yet, possibly due to the limitation of observational cadence.

scholarly journals Photospheric and “Chromospheric” CIV Lines in B-Main-Sequence Stars

1986 ◽  
Vol 116 ◽  
pp. 113-116
Author(s):  
Fiorella Castelli ◽  
Carlo Morossi ◽  
Roberto Stalio
Keyword(s):  
High Temperature ◽  
Stellar Wind ◽  
High Velocity ◽  
Main Sequence ◽  
Stellar Atmosphere ◽  
Uv Spectra ◽  
Spectral Lines ◽  
Early Type ◽  
Main Sequence Stars ◽  
Early Type Stars

The presence in the far-UV spectra of early-type stars of spectral lines of superionized atoms is argument of controversial debate among astronomers. Presently there is agreement on the non-radiative origin of these ions but not on the proposed mechanisms for their production nor on the proposed locations in the stellar atmosphere where they are abundant. Cassinelli et al. (1978) suggest that the Auger mechanism is operative in a cool wind blowing above a narrow corona to produce these ions; Lucy and White (1980) introduce radiative instabilities growing into hot blobs distributed across the stellar wind; Doazan and Thomas (1982) make these ions to be formed in both pre- and post-coronal, high temperature regions at low and high velocity respectively.

scholarly journals Exploring the Stellar Rotation of Early-type Stars in the LAMOST Medium-resolution Survey. II. Statistics

2021 ◽  
Vol 921 (2) ◽  
pp. 145
Author(s):  
Weijia Sun ◽  
Xiao-Wei Duan ◽  
Licai Deng ◽  
Richard de Grijs
Keyword(s):  
Velocity Ratio ◽  
Stellar Mass ◽  
Rotating Stars ◽  
Early Type ◽  
Stellar Rotation ◽  
Rotation Rates ◽  
Medium Resolution ◽  
Early Type Stars ◽  
The Difference ◽  
Chemically Peculiar Stars

Abstract Angular momentum is a key property regulating star formation and evolution. However, the physics driving the distribution of the stellar rotation rates of early-type main-sequence stars is as yet poorly understood. Using our catalog of 40,034 early-type stars with homogeneous v sin i parameters, we review the statistical properties of their stellar rotation rates. We discuss the importance of possible contaminants, including binaries and chemically peculiar stars. Upon correction for projection effects and rectification of the error distribution, we derive the distributions of our sample’s equatorial rotation velocities, which show a clear dependence on stellar mass. Stars with masses less than 2.5 M ⊙ exhibit a unimodal distribution, with the peak velocity ratio increasing as stellar mass increases. A bimodal rotation distribution, composed of two branches of slowly and rapidly rotating stars, emerges for more massive stars (M > 2.5 M ⊙). For stars more massive than 3.0 M ⊙, the gap between the bifurcated branches becomes prominent. For the first time, we find that metal-poor ([M/H] < −0.2 dex) stars only exhibit a single branch of slow rotators, while metal-rich ([M/H] > 0.2 dex) stars clearly show two branches. The difference could be attributed to unexpectedly high spin-down rates and/or in part strong magnetic fields in the metal-poor subsample.

scholarly journals Exploring the Stellar Rotation of Early-type Stars in the LAMOST Medium-resolution Survey. I. Catalog

2021 ◽  
Vol 257 (2) ◽  
pp. 22
Author(s):  
Weijia Sun ◽  
Xiao-Wei Duan ◽  
Licai Deng ◽  
Richard de Grijs ◽  
Bo Zhang ◽  
...  
Keyword(s):  
Early Type ◽  
Stellar Rotation ◽  
Medium Resolution ◽  
Early Type Stars

scholarly journals Observations of velocity fields in WN and Of stars

1979 ◽  
Vol 83 ◽  
pp. 475-478
Author(s):  
Virpi S. Niemelä
Keyword(s):  
Velocity Field ◽  
Large Scale ◽  
Velocity Fields ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Emission Lines ◽  
Temperature Structure ◽  
Early Type ◽  
Velocity Gradients ◽  
Early Type Stars

Systematic wavelength shifts of series of spectral line centers observed in many early type stars, generally interpreted as due to large scale motions, can give us information about the velocity gradients in stellar atmospheres. However, it should be borne in mind that the velocity gradients inferred from the observed displacements of spectral lines may not correspond to a unique alternative (e.g. see Karp 1978). Also, and especially when we are dealing with stars which have emission lines in their spectra, the structure of the velocity field depends on the assumed temperature structure of the atmosphere, i.e. in which atmospheric region do the lines originate.

scholarly journals On the perspectives of using XMM to study fundamental parameters of early-type stars

1999 ◽  
Vol 193 ◽  
pp. 90-91
Author(s):  
Gregor Rauw ◽  
Karel A. van der Hucht ◽  
Rolf Mewe ◽  
Manuel Güdel ◽  
Jean-Marie Vreux ◽  
...  
Keyword(s):  
Effective Area ◽  
Early Type ◽  
X Ray ◽  
Fundamental Parameters ◽  
Medium Resolution ◽  
Wide Range ◽  
Imaging Camera ◽  
Substantial Progress ◽  
Early Type Stars ◽  
Reflection Grating

Although substantial progress has been achieved since the discovery of X-ray emission from early-type stars with the EINSTEIN satellite, several crucial aspects of this phenomenon are still not fully understood. Considerable breakthroughs in this field are expected from observations with the X-ray Multi-Mirror satellite (XMM) due for launch in early 2000. XMM is the second cornerstone mission of the ESA Horizon 2000 science programme (see Lumb et al. 1996 and references therein for an overall description of the satellite). XMM offers a large effective area over a wide range of energies and its instrumentation provides simultaneously non-dispersive spectroscopic imaging (EPIC - European Photon Imaging Camera), medium-resolution dispersive spectroscopy (RGS - Reflection Grating Spectrometer) and optical-UV imaging (OM - Optical Monitor).

scholarly journals Mass-loss predictions and stellar masses of early-type stars

2003 ◽  
Vol 212 ◽  
pp. 164-165 ◽  
Author(s):  
Alex de Koter ◽  
Jorick S. Vink
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Spectroscopic Binaries ◽  
Evolution Theory ◽  
Early Type ◽  
Direct Measurements ◽  
Wind Theory ◽  
Early Type Stars ◽  
Stellar Masses

We show that the stellar masses implied by our predictions of the wind properties of massive stars are in agreement with masses derived from evolution theory and from direct measurements using spectroscopic binaries, contrary to previous attempts to derive masses from wind theory.

DISCUSSION ON THE SELF-ABSORPTION OF SODIUM 330.3 NM RESONANCE LINE FOR THE SPHERICAL GEOMETRY PLASMA

2010 ◽  
Vol 24 (21) ◽  
pp. 2267-2275 ◽  
Author(s):  
JIAN HE ◽  
LIXIN XIA
Keyword(s):  
General Expression ◽  
Calculation Method ◽  
Resonance Line ◽  
Spherical Geometry ◽  
Spectral Lines ◽  
The Self ◽  
The Real ◽  
Relationship Of ◽  
The Relationship ◽  
Escape Factor

In this letter, self-absorption is discussed using the concept of escape factor. The calculation method of the escape factor for spherical geometry plasma is discussed. For the spherical geometry, the escape factors Λ(r) at any position r in a spherical geometry plasma (with the radius R) for Lorentzian and Holtsmarkian profiles are calculated, and a general expression is obtained. As an example, for the sodium 330.3 nm resonance line, the total radiance and the real radiance are calculated, and the self-absorption for the resonance line is discussed. This discussion will be useful for the study of the relationship of escape factor and the self-absorption of spectral lines for any geometries.

scholarly journals The MASSIVE Survey – VII. The relationship of angular momentum, stellar mass and environment of early-type galaxies

2017 ◽  
Vol 471 (2) ◽  
pp. 1428-1445 ◽  
Author(s):  
Melanie Veale ◽  
Chung-Pei Ma ◽  
Jenny E. Greene ◽  
Jens Thomas ◽  
John P. Blakeslee ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Stellar Mass ◽  
Early Type ◽  
Relationship Of ◽  
The Relationship

scholarly journals The Early-type Stars from the LAMOST Survey: Atmospheric Parameters

2021 ◽  
Vol 257 (2) ◽  
pp. 54
Author(s):  
Yanjun Guo (郭彦君) ◽  
Bo Zhang ◽  
Chao Liu ◽  
Jiao Li ◽  
Jiangdan Li ◽  
...  
Keyword(s):  
High Resolution ◽  
Massive Stars ◽  
Rotational Velocity ◽  
Training Data ◽  
Early Type ◽  
Atmospheric Parameters ◽  
Data Set ◽  
Medium Resolution ◽  
I 11 ◽  
Early Type Stars

Abstract Massive stars play key roles in many astrophysical processes. Deriving the atmospheric parameters of massive stars is important to understanding their physical properties, and thus the atmospheric parameters are key inputs to trace the evolution of massive stars. Here we report our work on adopting the data-driven technique called stellar label machine (SLAM) with the nonlocal thermal equilibrium TLUSTY synthetic spectra as the training data set to estimate the stellar parameters of Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) optical spectra for early-type stars. We apply two consistency tests to verify this machine-learning method and compare stellar labels given by SLAM with the labels in the literature for several objects having high-resolution spectra. We provide the stellar labels of effective temperature (T eff), surface gravity ( log g ), metallicity ([M/H]), and projected rotational velocity ( v sin i ) for 3931 and 578 early-type stars from the LAMOST low-resolution survey (LRS) and medium-resolution survey (MRS), respectively. To estimate the average statistical uncertainties of our results, we calculated the standard deviation between the predicted stellar label and the prelabeled published values from the high-resolution spectra. The uncertainties of the four parameters are σ(T eff) = 2185 K, σ ( log g ) = 0.29 dex, and σ ( v sin i ) = 11 km s − 1 for MRS, and σ(T eff) = 1642 K, σ ( log g ) = 0.25 dex, and σ ( v sin i ) = 42 km s − 1 for LRS spectra, respectively. We note that the parameters of T eff, log g , and [M/H] can be better constrained using LRS spectra than using MRS spectra, most likely due to their broad wavelength coverage, while v sin i is constrained better by MRS spectra than by LRS spectra, probably due to the relatively accurate line profiles of MRS spectra.

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